Atomic　clock　difference　prediction　is　the　key　step　in　atomic　clock　time　scale　generation　and　atomic　clock　control.　The　atomic　clock　is　a　precise　signal　source,　and　its　signal　consists　of　the　determined　signal　part　which　is　corrected　by　the　prediction　algorithm　and　the　inherent　noise,　which　is　a　random　part.　The　hydrogen　and　cesium　clock　mainly　contain　two　kinds　of　noise,　that　is,　white　frequency　noise　and　random　walk　frequency　noise.　These　two　kinds　of　noise　are　the　main　factors　that　produce　the　uncertainty　of　prediction.　The　mathematical　expression　of　the　prediction　uncertainty　of　the　time　difference　data　of　the　atomic　clock　is　derived,　based　on　the　mathematical　model　of　the　atomic　clock,　and　the　minimum　prediction　uncertainty　of　the　clock　group　is　obtained.　The　influence　of　the　number　of　clocks　in　the　clock　group　on　the　prediction　uncertainty　is　analyzed.　Finally,　the　correctness　of　the　theory　is　verified.　©　2019,　Acta　Metrologica　Sinica　Press.　All　right　reserved.